基于m序列的OFDM二阶时频同步算法

A Two-stage Tim and Frequency Synchronization Method for OFDM Systems Based on m-sequence Preamble

针对S&C方法的定时平台和Minn方法出现多个峰值的不足,设计了一种基于m序列具有四重重复反对称的结构。提出一种基于本训练序列的OFDM二阶时频同步算法:粗同步和精同步。在粗同步时,利用训练序列的特殊结构,采用延时相关确定粗同步的定时位置,在此位置的前后小范围内利用m序列及其循环移位序列与接收数据进行差分相关算法,完成精同步定时。继而利用训练序列的延时相关求得小数频偏估计。仿真结果显示,在多径衰落信道下,与已有算法比较,所提出的二阶算法定时准确,频偏估计性能良好,尤其在信噪比较低时采用该算法能实现更准确的同步。

In order to reduce the time synchronization plafform of S＆C algorithm and side-peak of Minn algorithm,a new two-stage time and frequency synchronization for OFDM systems was proposed which approach exploited a single-symbol preamble with a repetitive structure,composed of four identical m-sequences with an inverse polarity for the first half part and the latter half part.The first stage,coarse stage,the auto-correlation was used to finish synchronization based on the special structure of preamble.The second stage,fine stage,the differential correlation was used to find a more accurate timing location around the timing position of the coarse stage.The fractional frequency offset estimation was accomplished by auto-correlation of the repetitive preamble after the time synchronization has been done.The simulation results prove that,compared to existing algorithms,the accuracy of time synchronization and the fractional frequency offset estimation are greatly enhanced in multipath fading channel,even at very low SNRs.